The present disclosure relates generally to surgical guidance.
Image-guided target tracking and surgical guidance is a method for locating a specific target within three-dimensional (3D) space. This technique is routinely used in medical procedures to locate an object in the human body, such as the spine, brain or other organ structures, during surgery.
One approach to a guided surgical intervention includes the use of fiducial markers that are attached to the body with a clamp, an adhesive, or through other means. Generally, these fiducial markers are aligned to a 3D representation of the body, which may be acquired by different imaging modalities. This 3D representation, usually acquired before surgery, may include a specific region, such as a vertebral column, to a scan of the entire body. Within this 3D representation, areas of interest are located and matched to the fiducial markers in the real surgical space. This results in a coordinate system transform that maps the relative position of the region of interest to the location of the fiducial markers to provide visual feedback to the clinician during surgery. The surgeon can then use this information to facilitate guidance to a specific location in the body that is related to the region of interest in the image.
Optical-based surgical navigation has been used for the past decade to guide spinal surgeries and, in particular, placement of screws in the spine. These systems are based on two cameras that detect light that is either emitted (mounted with LEDs) as disclosed in U.S. Pat. No. 5,921,992, or passively reflected from surgical tools and probes as disclosed in U.S. Pat. No. 6,061,644. Using the signal detected by the cameras combined with the knowledge of the dimensions of the navigation probes, a computer workstation is able to precisely determine where the tip of the surgical instrument lies.
U.S. Pat. Nos. 5,531,520 and 5,999,840 provide a system that utilizes a plane of laser light and a video camera to obtain three-dimensional measurements of the patient's skin, where the system employs the “structured light” method of obtaining the desired measurements for registration of 3D pre-operative image data. Prior to a surgical procedure, pre-operative MRI or CT data is first obtained. Subsequently, in an operative setting, the patient is scanned by a laser range scanner. The pre-operative MRI or CT scan is automatically registered to patient skin surface obtained by the laser range scanner, providing a transformation from MRI/CT to patient. The position and orientation of a video camera relative to the patient is determined by matching video images of the laser points on an object to the actual 3D laser data. This provides a transformation from patient to video camera. The registered anatomy data is displayed in enhanced visualization to “see” inside the patient.
The registration process taught by U.S. Pat. No. 5,999,840 also discloses the tracking of surgical instruments and probes. A probe is tracked by a separate probe tracking system, in which dedicated probe tracking cameras are employed to track a probe. The tracked probe data is then registered to the three-dimensional skin surface data using a calibration process. Thereafter, the data registration between the probe and the skin surface is used to provide visualization information to the surgeon.
In order to track the probe, a calibration procedure is needed to register the reference frame of the probe tracking system to that of the optical surface measurement system. This calibration process involves the measurement of a calibration object. The process requires that the probe tracking reference frame be fixed relative to the optical surface measurement system to maintain calibration, such that the optical surface measurement system cannot be moved relative to the probe tracking reference frame intraoperatively. This requirement can constrain surgical workflow and cause a need for inter-operative re-calibration of the system.